DE 20 2004 015 442 U1 shows an air heater for a vehicle, in which a heat exchanger assembly unit is connected to a blower assembly unit in the area of sealing surfaces located opposite each other. The heat exchanger assembly unit comprises a heat exchanger housing, which is made, for example, of a cast metallic material. The heat exchanger housing has a combustion chamber assembly unit mounting space, in which a combustion chamber assembly unit to be fed with combustion air and fuel can be accommodated. The combustion waste gases generated during the combustion in the combustion chamber assembly unit flow into a heat exchanger area, which follows the combustion chamber assembly unit mounting space and which has heat transfer ribs enlarging the heat transfer surface on both its inner side for thermal interaction with the combustion waste gases and its outer side for thermal interaction with the air to be heated.
The blower assembly unit comprises a blower housing, which carries or accommodates a blower motor on its side facing away from the heat exchanger assembly unit and has a delivery channel, which is open in the direction of an axis of rotation of a delivery wheel and surrounds the axis of rotation of the delivery wheel in a ring-shaped manner on its side facing the heat exchanger assembly unit. The delivery wheel covers the delivery channel and is located essentially in the combustion chamber assembly unit mounting space of the heat exchanger housing, which said mounting space also accommodates the combustion chamber assembly unit. The blower assembly unit designed in the manner of a side channel blower delivers the air necessary for the combustion into the combustion chamber assembly unit mounting space and consequently in the direction of the combustion chamber assembly unit.
To produce a tight connection of the combustion chamber assembly unit to the heat exchanger assembly unit, sealing surfaces of these assembly units are located opposite each other via the intermediary of a sealing element. These two housings are braced against one another via the intermediary of the sealing element by a plurality of bolts connecting the blower housing to the heat exchanger housing. In general, thin sealing elements consisting of a comparatively hard material, for example, rubber-coated metal seals, are inserted in the area between the blower assembly unit and the heat exchanger assembly unit. Since the delivery wheel is positioned in the blower assembly unit at a very short distance above the blower housing having the delivery channel, it is necessary to manufacture the blower housing with high precision. To avoid generating a deformation of the blower housing, which is made, for example, of an aluminum material, when assembling the blower housing with the heat exchanger housing via the intermediary of the sealing element, the two sealing surfaces, which are positioned opposite each other via the intermediary of the sealing element and are pressed against one another, also must be provided with correspondingly high precision. This is achieved, in general, by subjecting the blower housing in its area covered by the delivery wheel and in the area of the sealing surface provided thereon and the heat exchanger housing in the area of the sealing surface provided thereon to a finishing operation by machining.